In an image forming apparatus of an electrophotographic type, toner is stored in a development device constructing a process unit, transported from a supply roller to a development roller of the development device, and supplied to a photoreceptor drum through the development roller. A section that performs toner supply to the photoreceptor drum is arranged with an opening of the development device so as to supply toner toward outside from inside of the development device. Such a section or region that performs toner supply to a photoreceptor drum through a development roller is hereinafter referred to as a development region.
It is required to efficiently supply toner to a photoreceptor drum in a development region, while leakage of toner from other sections must be avoided because toner splash affects the exposure optical path and causes contamination of the inside of an image forming apparatus, including a charger. Therefore, sealing is applied to gaps of a development device, from which toner is preferably prevented from leaking.
In many cases, gaps formed between components of a development device have complicated shapes. Accordingly, in order to seal such sections, members for sealing (hereinafter, also referred to as sealing members) to fit a complicated shape are required. In such a situation, sealing members are forced to have a complicated shape. Forming such a sealing member into one body increases the difficulty of making the sealing member, and further, it becomes difficult to incorporate it to a portion of a gap, from which leakage of toner is to be avoided. Accordingly, it is practical to produce several divided sealing members, incorporate the sealing members in a combination at a desired section of a development device, and thus sealing is done.
As examples of concrete technologies for the purpose of prevention of toner leaking to outside of a process unit, Patent Document 1 (Japanese Patent Publication TOKKAI No. H11-316500) discloses a technology in which a protrusion is provided at a portion where a side seal and bottom seal of a development roller are superposed with each other, and Patent Document 2 (Japanese Patent Publication TOKKAI No. 2000-75656) discloses a technology which specifies the shape of an end portion of a lower seal in a region where a development roller and a side seal are superposed with each other.
However, the above development device, having a structure which is sealed such that several divided sealing members in a combination are incorporated at a desired section of the development device, may be insufficiently prevented from toner leakage at the jointing section of the combined sealing members. In other words, a structure in which end surfaces of the sealing members are brought into contact with each other tends to cause a gap between end surfaces of the sealing members that are brought into contact with each other, and accordingly toner leaks through the gap once it is generated.
Further, even in a case where a structure with superposed sealing members in a combination at the jointing section is employed so as to prevent generation of a gap between end surfaces of sealing members at the jointing section, a step may be generated at the boundary section of the superposed sealing members, and toner may leak through the step. As described above, for a structure for sealing by incorporating a combination of several divided sealing members at a desired section of a development device, sealing members can be easily produced and incorporated, but there is still a problem to be solved for prevention of toner leakage.
An object of the present invention is to provide a development device having a structure for sealing at a desired section of the development device by incorporating a combination of several divided sealing members so as to prevent leakage of toner from the jointing section of the sealing members.